Case Report Support by Potato Dextrose Agar for Fungal and Bacterial Growth at ۴oC

Potato Dextrose Agar (PDA) has a potential to support the growth of bacteria and fungi and for isolation as well as enumeration of not only moulds but also yeasts. It is a cream to yellow colored medium that gets solidified in the petri dish when excess bacterial agar (۳gm/۱۰۰ml) is mixed prior to autoclaving. Its composition for ۱ litre is as follows: potatoes, infusion-۲۰۰ grams, dextrose (glucose)-۲۰grams, agar-۱۵ grams and pH at ۲۵oC is ۵.۶±۰.۲.The medium/refrigerator product for preservation is kept in the refrigerator at ۴oC for preservation till the use. During the preservation, it is expected that the medium should should be stable and contamination free. However, there is a shelf life to the PDA for storage in the refrigerator. After expiry of the refrigerator period, it gets dried rendering its uselessness for the further application. However, we reported unexpected observation on ۱th October ۲۰۲۲. We made ۲۰۰ ml PDA agar on ۱۰th August ۲۰۲۲ using a ready to use bottle of a Himedia, autoclaved it at ۱۲۱ oC for lb pressure for ۲۰ minutes as per the sterilization guidelines and poured in the ۱۰ petri dishes in aseptic condition and then kept the medium for solidification for ۳۰ minutes. After words, we placed the plates for refrigerator at ۴oC. Then, we kept it under supervision and shocking, it was reported that the growth of black-white colored fungi (figure no۱a) white colored fungi (figure ۱c,۱d) and pink colored bacteria (figure ۲a, ۲b) were observed with their luxuriant growths. The staining of fungi by lactophenol blue of black-white fungi (figure ۱b) and white fungi (figure ۱e) showed mycelium threads.To add, we performed gram staining of the reported bacteria with pink colonies (figure ۲c) and found that they were gram positive cocci. Interestingly, they also contaminated the green (figure ۳) and white (figure ۴) fungal culture preserved at ۴oC for one month. In this case, we conclude that the PDA under study has been not protected at ۴oC for ۵۲ days from the psychrophilic growth raising the question on its efficiency and efficacy for long term preservation of microbial cultures suggesting an urgent need to search either alternate medium or updating the composition of it.

کلیدواژه ها:

Potato Dextrose Agar Medium ، Hi Media Product ، Fungus ، Bacteria